STUDIES ON INITIATION AND DEVELOPMENT OF THE PARTNER ASSOCIATION IN GEOSIPHON PYRIFORME (KUTZ) V WETTSTEIN, A UNIQUE ENDOCYTOBIOTIC SYSTEM OF A FUNGUS (GLOMALES) AND THE CYANOBACTERIUM NOSTOC-PUNCTIFORME (KUTZ) HARIOT

Phagocytosis of Nostoc filaments by Geosiphon, a fungus closely relate d to AM forming Glomales, was observed under light microscopes. Incorp oration can only be performed if Nostoc primordia come into contact wi th growing hyphal rips of the fungus. The fungal wall just below the a pex softens, and fungal cytoplasm is bulged out repeatedly covering th e vegetative Nostoc cells but not the heterocytes. New heterocytes are differentiated by the internalised filament whose cells can increase up to ten times in volume after recovering from incorporation strain. The Nostoc cells are coated stepwise by short finger-shaped protuberan ces of the fungal hypha. These hernia-like outgrowths first remain sep arated, after 1 to 2 days they merge. Adjacent hyphal walls inside the complex covering disintegrate. Periphal fungal wall portions are unit ed to form a smooth strong outer envelope. Internalisation is categori sed as phagocytosis. The partnership is partly specific, Nostoc strain s capable of living endocytobiotically are often partners in other sym bioses besides Geosiphon.